I went shopping for eyeglasses last weekend with my friend Lisa Ferber, as I'm following my readers’ advice about taking along a trusted friend in order to find a pair that suits me. She patiently watched and advised as I tried on dozens of pairs of glasses throughout the afternoon. The routine was: I'd try on a pair, look at her, look at the glasses clerk, and then look in the mirror. And every time I’d look in the mirror, Lisa would say, “No pouting.” This went on for about an hour, until finally she forbade me to stop making my “mirror face” for the rest of the day—not that her directive helped, because it’s utterly beyond my control.

I’ve written about my mirror face before (unsurprisingly, when I was doing my mirror fast). But this was different, and it took me a while to realize why. When I looked in the mirror at my bespectacled self, I thought I was giving myself the same look that I’d just given my friend. I was able to believe that because the face I saw reflected back at me wasn’t my usual, and private, mirror face—another expression I can’t control, but that I can easily spot as ridiculous. This was less pouty (Lisa’s protest notwithstanding), a little more grim, a little harder, the jaw a little more set. Unlike my mirror face, which is a subconscious attempt to control how I see myself, this face was an attempt to not look as though I knew I was being observed. This face was supposed to be natural.

It wasn’t natural, of course—far from it. But it might be innate. I saw my public mirror face crop on on the faces of total strangers in this project by Swedish photojournalist Moa Karlberg, who set up a camera behind a one-way mirror and photographed subjects looking at themselves, unaware they were being photographed. (Thanks to Caperton at Feministe for the link.) Karlberg’s written intention for the series indicated that she wanted it to be a comment on privacy rights in public spaces. But the takeaway is something quite different.

We think we’re seeing people’s private moments exploited for our viewing pleasure, lending an edge of voyeurism above and beyond normal portraiture. Here’s the thing, though: These photographs were not taken in private homes or even in restrooms or other spaces with an expectation of privacy; they were taken in public. The subjects all believed they were having a semi-private moment, true, but they also knew they might be observed by passersby. They couldn’t have known that Karlberg was on the other side of the mirror, of course, but in some ways that doesn't matter. The law of physics that states that observation changes that which is being observed applies double to the mirror: We change when we look into the mirror, and we change yet again when we know someone else might observe us doing so. (Certainly I can't be the only person who has ever dawdled in a work bathroom in hopes that the other people present will leave so I can observe myself in peace. Um, if I am the only person who has done this I will be officially embarrassed.)

What’s striking about the photographs is how most of the people in them are wearing a nearly identical expression—across ages, across genders, across cultural types. Examining that expression, I’m drawn to the pensive defiance on the subjects’ faces. The mouth is slightly open, a steely expression in the eyes. To me, what this says is: I am not actually looking at myself; I merely happened to catch a glimpse of myself while walking by. (And, after a month of avoiding mirrors, I can tell you that the unaware glimpse does occasionally happen—and that most of the time there’s a reflective surface around, you damn well know it.) The feigned nonchalance is a part of how we make our way through the world; it’s how we avoid seeming to think that we’re overimportant, or self-absorbed. It’s the equivalent of a big, surprised “Oh, hi!” we give an acquaintance we’d spotted earlier in a crowd but delayed saying hello to for whatever reason. It’s the face we wear when we’re walking down an long hallway toward a coworker but aren’t yet close enough to acknowledge their presence without creating awkwardness. It’s neither private nor public; it’s a performance that you hope nobody sees but are certain to perfect in the event that they do.